Week 8 (Sep 23 - Sep 27)

Monday

As per described on Week 7 (Sep 17 - Sep 20) Tuesday's list of activities, the PDMS was finally put into some molds and left to cure wrapped in aluminum foil at 70°C overnight. Only 5 molds were filled to test for shape and ease of retrieval. They will be retrieved on Tuesday morning. An updated version of the activities list is shown below.

Activities for the week

~~Retrieve and check PDMS cylinders~~
~~Fill the rest of the molds and cure PDMS~~
~~Cut PMMA if cylinders don't fit the current bottom layers~~
~~Fabricate new device and test for fitting and leakages~~

Furthermore, if there is enough time throughout the week, some additional yet important tasks could be done.

Additional tasks

Perform chemical modifications on PDMS cylinder substrates (triplicates yet again)
Check modification retainence on the surface before and after insertion in bottom layer

Tuesday

New bottom layers were cut and PDMS molds were filled and left to cure overnight. It is expected that the molds will help the PDMS maintain a good shape for the substrate to completely seal the air chamber and prevent any leakages.

Wednesday

The PDMS substrates were retrieved. Upon 3 tests, the best way to remove them is to separate the piece from the walls of the cylinder mold using pointy tweezers. Then, when most of it has separated, push the substrate out.
The device was successfully fabricated. The PDMS substrate was slightly bigger than the hole, so there is some effort required to fit it inside the device. However, it can be done in a way that most of the surface remains untouched during the process, which will be further confirmed with modification experiments.
First, an issue must be addressed: the thickness of the middle layer, which gives height to the middle layer, is very small. With the insertion of the PDMS substrate, the surface ends up touching the internal face of the top layer, which can potentially damage the surface modification.

Successes

Fabricated PDMS cylinders that fit into the holes
No leakages were found in the device
Reciprocation was achieved

Issues found

Due to the insertion procedure of the PDMS substrate, surface touches the top layer. Modifications might get damaged

Solution of issues

Middle layer of 1mm and holes on bottom layer closer to entrance can lead to better performance with the same sample volume

Flow reciprocation was achieved. To test for both leakages and reciprocation, the device was spun. If no sign of leakage was perceptible, the device was stopped and the recession of the fluid was observed.
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Thursday

Alternative solution

A different approach to avoid increasing the size of the air chamber can be changing the method of insertion of PDMS

PDMS will be inserted by twisting and pushing instead of just pushing
This method might make the insertion process more controllable, allowing for a better leveling of the modified surface.

Success

It is possible to introduce and control the PDMS cylinder substrate by rotating it while pressing.

Non-uniform placement

Although it is possible to fit the PDMS cylinder substrates into the bottom layer holes, they are a lot wider, considering the scale of operation, than the holes, making it difficult to place it as leveled as possible.
Fluid can go above the PDMS piece, but due to improper alignment and leveling, the pressure can lead to eventual leakage after some reciprocation cycles.

Substrate damaging

After a few attempts of fitting a substrate, the edges and sides of the cylinder get damaged due to the size difference
Experiments of chemical modifications have demonstrated that, upon cleaning, the substrate can be modified again, but it gets difficult to reuse if substrate gets damaged.

Decrease internal size of PDMS molds

Measurements will be taken to reduce the size of PDMS molds to make thinner cylinders to make it easier to place, but with enough tolerance to make the device leakage-free

Increase size of PMMA hole

Alternatively, a knife can be used to increase the size of the already existing holes. This is to avoid wasting material and use the already cut pieces